Flame propagation and quenching in iron dust clouds

Laminar flames propagating in fuel-rich suspensions of iron dust in air were studied in a reduced-gravity environment provided by a parabolic flight aircraft. Experiments were performed with four different dusts having average particle sizes in the range 3–27 μm. Uniform dust suspensions were created inside glass tubes (ID = 48 mm, L = 70 cm) and then ignited at the open end via an electrically heated wire. Quenching distances were determined as the flames propagated through assemblies of equally spaced steel plates installed in the tubes. Flame propagation speeds in the open tubes and within the quenching plates were determined from video recordings, and emission spectra recorded by a spectrometer were used to determine flame temperature. Flame quenching distance was found to increase linearly with particle size from less than 2 mm quenching distance for the 3 μm-sized dust to 10 mm quenching distance for the 27 μm-sized dust. The flame speeds in the open tubes were found to be inversely proportional to the dust particle size, and the minimum speeds observed near quenching within the plate assemblies were found to be a factor of smaller than the flame speeds in the open tube. The experimental results were in good agreement with the predictions of a simple one-dimensional dust flame model with conductive heat loss that assumes the diffusive regime of particle combustion.